Decentralized Poly-generation of Energy: Basic Concepts - Design for Micro-Combined Cooling, Heating and Power Systems - page 50

The energies produced by the CCHP system are dependent on the type of
refrigerating device, but also on whether the system is connected to the national
electricity grid or not.

3.1 Energy Conversion in the Trigeneration

Note electric energy as E, the thermal energy for heating the residence as Q, the
energy necessary for the air conditioning of the residence as C, and the thermal
energy for preparing domestic hot water as Q hw . To satisfy the demand for electric
energy of the residence, the following systems may be used:

Centralized energy producing system. In this case, the residence is connected to
the electricity grid. The thermal energy demand for heating the residence or for
cooling the air in the residence must be ensured with a system which contains
equipment installed in the residence. This system includes a conventional
condensing boiler (with 90 % thermal ef

￿

ciency) providing heat for space
heating and sanitary uses (hot water), and a conventional compressing refrig-
erator which supplies cold for air conditioning (Fig. 10 ).
Regarding the cooling equipment, performance is usually described by means of
the speci

ned
as the ratio of the desired cooling energy output to the relevant input (electrical
energy for electric chillers).
The energetic balance of this system is:

c coef cient of performance (COP). The COP C can be generally de

for the electric subsystem:

￿

C
COP C

E grid ¼ E þ ð 8 Þ

E grid E

Imported/
electricity

Electricity need

Cold for space
conditioning
(summer)

C

Compressing
chiller

Q b

Heat for space
heating (winter)
Hot water (summer)

Condensing boiler

Natural gas

Fig. 10 Centralized energy producing system